Chapter 12 — Key Takeaways
A scannable one-page card. If you remember nothing else from this chapter, remember that price is only half the deal — structure is the other half, and it is the half that turns a marginal risk into an account you can write profitably.
The core claims
- Structure makes a risk writable that price alone cannot. A senior underwriter rarely declines outright; they ask at what terms would I write this? Two policies at the same premium can be wildly different bets depending entirely on how they are structured.
- Every structural feature does double duty: it slices the cost of a loss and engineers the insured's incentive to prevent it (the moral/morale-hazard logic from Chapter 1).
- The catastrophe peril needs its own tool. A flat deductible fails on a correlated loss; the percentage (catastrophe) deductible is indispensable for coastal and quake-exposed property.
- Some structures transfer a credit risk, not an insurance risk. SIRs and large deductibles hand the insured a layer — but where the insurer fronts statutory/third-party payments, it is lending, and must be secured with collateral that is re-evaluated as exposure develops.
- Coinsurance polices under-insurance; it does not prevent it. It is a backstop, not a substitute for getting values right at underwriting. Where valuation certainty matters, write agreed value (Ch. 19).
- The binder binds exactly what it says. The most expensive structuring error is a subjectivity or restriction left off the binder — an omission grants the broader coverage.
The toolkit, in the order you reach for it
| Tool | What it does | The trap |
|---|---|---|
| Deductible (per-occ / aggregate / %) | Sheds small losses, lowers price by retained expected loss, preserves incentive | A flat deductible on a catastrophe peril is a rounding error |
| SIR / large-deductible program | Hands the insured a whole layer; trades premium for the insured's credit risk | Censored loss history + the insured's solvency you must monitor |
| Limits (per-occ / aggregate) | Cap where the insurer's payout stops | Liability aggregates bite — one bad year can exhaust them |
| Sublimit | Says "yes, but only this far" to one exposure | Forgetting that the un-sublimited perils still carry the full limit |
| Coinsurance clause | Penalizes under-insurance on every partial loss | Relying on it instead of underwriting the value |
| Endorsements (restrict / broaden) | Carve out a hazard / fill a gap | A restriction the insured never registered = a coverage dispute |
| Manuscripting | Writes the risk no standard form fits | Every word is construed against the drafter (contra proferentem) |
| Binder / coverage letter | Make the deal real (grant / offer coverage) | An omitted condition on the binder grants broader coverage |
The key formula
Coinsurance loss payment:
$$\text{Loss} \times \frac{\text{Insurance carried}}{\text{Insurance required}} - \text{deductible}$$
where insurance required = coinsurance % × full value at time of loss. If carried < required, the insured becomes a coinsurer of its own loss — even a partial one far below the limit.
Deductible credit rule of thumb: raising a deductible saves the insured the expected loss in the retained layer (plus a claims-expense credit) — not the full additional retention.
Key terms
deductible · self-insured retention (SIR) · per-occurrence vs. aggregate limit · sublimit · coinsurance clause · binder · large-deductible program
What you could defend to your manager
"I didn't decline Harbor Steel's catastrophe exposure — I structured it. A 5% named-windstorm deductible puts \$1M of every storm loss back on the insured and off our coastal book; a separate AOP deductible handles the fire frequency; an ACV-roof endorsement carves out the worn-out roof until they replace it; and I wrote the property on agreed value so a partial fire loss is never reduced by a coinsurance penalty. Same risk, same insured — a policy that fits, priced for what it actually carries. The decision and the subjectivities are Chapter 13's; the terms are built and defensible."